Fel stalkers are the hunting hounds of the pit lords, starving both for blood and for arcane energy. The corner of the Twisting Nether that spawned them is a void, drained of magic and substance and filled with drifting corpses. Maggot fel stalkers embedded in the nearby planar substance mature, hunt, and often lay young before the pit lords rangers find them and train them. Fel stalkers have been observed with 2, 4, or 6 legs which indicates breed rather than power. Fel stalkers treat spellcasters, particularly arcane spellcasters, as layered desserts with meat on the outside and magic on the inside. Less magical characters are worth notice only if they have damaged the fel stalker in battle. Fel stalkers generally use their arcane vortex ability whenever in combat, unless instructed otherwise by their pit lord.[1](MoM 122)

Fel stalkers tend to grow larger after feeding, they can also reproduce via mitosis after it has absorbed a sufficient amount of energy.[2](WoE 203)

Fel stalkers are demon hounds used by the pit lords to sniff out sources of magic wherever they be found. Felhounds, who feed upon magic itself, using the two tentacles on its back, are fond of draining the energies of hapless wizards, turning them into dry husks. They then rip the remains to shreds.

During the first Burning Legion invasion, the felhounds were commanded by Hakkar the Houndmaster. With a crack of his magic whip, he could summon them into existence from the demonic plane.

Besides draining magic, they can in fact eat meat and do defecate, as seen in Shizz Work.

In-game, fel stalkers are one of the few demon-typed creatures that can be skinned.